A North Texas woman is fighting for tougher charges against the man police say killed her grandson.

Three-year-old Tanner Webb died last October while in the care of his stepfather in Roanoke.

The child's grandmother, Shelly Hastings, wants the Denton County District Attorney to charge the boy's stepfather with capital murder, which carries a possible death penalty.

Currently the stepfather, Russell Miller, is charged with felony injury to a child. It carries a maximum penalty of life in prison.

"He's a monster. He's a complete monster," Hastings said of Miller. "He beat him over and over and over again."

Jamie Beck is an Assistant District Attorney in Denton County. "For the state to prove capital murder would be very difficult," she said. "You have to prove intent for little Tanner to die."

But the boy's grandmother hopes to convince the D.A. to increase the charges later this month. She plans to hold a candlelight vigil at Our Garden of Angels, a Fort Worth memorial which displays white crosses with the names of murder victims.

Russel Allen Miller pleaded guilty Friday in a Denton County district court to using a deadly weapon to injure his 3-year-old stepson, Tanner Webb, who had 43 external injuries when he died last year.

The 23-year-old Roanoke man agreed to a plea deal that would imprison him for 50 years  a deal favored by Tanner's mother, prosecutors said. Mr. Miller wouldn't be eligible for parole for 25 years.

"She did not want the case to go to trial," first assistant district attorney Jamie Beck said of Tanner's mother. "That would have been difficult for her. We got a quick resolution."

Mr. Miller's attorney could not be reached for comment.

Tanner died Oct. 21, shortly after Mr. Miller  who was alone with the boy  called 911 to report that he had stopped breathing.

"Me and my son were playing," Mr. Miller told the 911 operator in a recording obtained by The Dallas Morning News. "I was swinging him, and he hit his head on the couch, and he won't wake up. ... I don't want y'all to think the wrong idea because he looks like crap. He looks like he got beat."

"He's an absolute danger," Ms. Hastings said. "To do what he did to that little baby's body ... If he ever gets out on the street again, no one is going to be safe."

Prosecutors have said they couldn't prove Mr. Miller intended to kill Tanner  a requirement in a capital murder case. Ms. Beck said Friday that the genitalia wounds could not be tied to Mr. Miller "beyond a reasonable doubt."

The district attorney's office prosecuted Mr. Miller for injury to a child with an unknown deadly object. Ms. Beck said evidence shows Mr. Miller used his hands, which can be considered deadly objects, along with something else.

On the 911 recording, Mr. Miller speaks in a weeping voice and refers to the dispatcher as "ma'am." Tanner can be heard gurgling in the background between long gaps of silence as Mr. Miller performed CPR under the dispatcher's direction.

Mr. Miller told the dispatcher he had been swinging Tanner in circles, holding him by his shirt and pajama pants, when Tanner's head accidentally struck a couch. He also said Tanner had black eyes and a swollen forehead.

Investigators later concluded that the couch could not have caused the injuries. Flower Mound police, who cover the Roanoke neighborhood, arrested Mr. Miller a day later.

The medical examiner determined that Tanner died from blunt-force trauma to the head and ruled the death a homicide. But examiners also found 43 external injuries  from the boy's left heel to his face, including multiple head hemorrhages.

Ms. Hastings said she was upset that the court allowed only Tanner's mother, Destinee Ashton-Miller, to speak at Mr. Miller's hearing on Friday.

Ms. Hastings said Ms. Ashton-Miller should also face charges in Tanner's death. Ms. Hastings said the mother must have known Mr. Miller had been harming Tanner and didn't do anything about it.

"I'm not going to let her walk away unscathed," Ms. Hastings said. "If they don't pursue her criminally, I will file a civil suit."

Ms. Ashton-Miller could not be reached for comment.

Ms. Beck said prosecutors have spoken to Ms. Hastings and do not have any evidence to pursue criminal charges against Ms. Ashton-Miller.

"We looked, and we were willing to go there if the evidence pointed us there, but there's nothing," Ms. Beck said.

Injury to a child is a first-degree felony with a sentence of five years to life in prison. Ms. Hastings said she was relieved that Mr. Miller would serve at least 25 years, and added that her family would fight to make sure he's never paroled.

"Everything Russel has for the rest of his life  parole hearing, court date, whatever it is  we will all be there," Ms. Hastings said. "I will see to it, if I have my way, he will serve every one of those 50 years."